A variety of different types of X-ray measurements are possible for analysing materials. In an X-ray fluorescence measurement, a beam of X-rays is directed at a sample and the resulting X-rays emitted by the sample are measured by an energy dispersive X-ray detector. Such a detector measures X-ray intensity as a function of energy or equivalently as a function of wavelength.
For homogenous samples, including large crystalline structures, the sample area measured is often not critical. However, some samples such as powder mixtures and others can be inhomogeneous. Alternatively, X-ray measurements may be carried out to measure the inhomogeneity across a sample. In such cases, there is a need to measure X-ray emissions from a small sample spot.
A known approach to such measurements is to use a double pinhole collimator to select an X-ray spot. One option is to place the double pinhole collimator between the X-ray source and the sample. Only X-rays passing through both pin-holes reach the sample so the sample is illuminated only over a small spot. In another approach, a double pinhole collimator is used between the sample and the detector. In this case, only X-rays emitted from a small spot on the sample reach the detector. For example, using a 0.2 mm pinhole and a 0.36 mm pinhole 85.5 mm apart directly in front of a detector 160 mm from the sample a spot size of 0.71 mm diameter can be measured.
The problem with this approach is that the intensity of X-rays from the small spot is limited. Therefore, measurement can take a significant time and result in increased irradiation of the sample.